The tracking, i.e. the continuous detection, of the position of a component driven by an electric motor can be of importance in many areas. In automotive engineering, different motor vehicle components are driven by means of an electric motor such as for example windows, sunroofs, but also seats or sliding doors. In a similar manner, the current position of movable components in buildings, for instance of driven sliding doors, windows, awnings, venetian blinds, etc. is very interesting and must be detected. The position of the driven component in motor vehicles is of particular significance in so far as a jam protection system is usually required in the case of window lifters or sunroofs and, as a result, monitoring the position becomes more important the more the component approaches a closing position because in the case of an increase in the drive force or the closing force, it may close on a jammed object. A further aspect is the fact that in the case of such components such as window lifters or sunroofs, but also motor vehicle seats with a memory function, an automatic movement to the desired position takes place, unless there is a risk of injury, the automatic drive then being stopped and switched over to a manual movement control.
In order to be able to continuously detect the position of window lifters, it is customary to use the sensor means acting on the rotational movements of the electric motor fed by means of the battery of the motor vehicle, namely Hall sensor means or sensor means detecting current ripple signals, it being possible that the mentioned current ripple signals in the motor current were brought about by means of the commutation of the motor. This detection of the current ripple signals and their count are also referred to as the ripple count (current ripple signal). In detail, changes in the current overlapping each other are detected in this process, said changes in the current being generated in the case of commutations in the brushes of the direct current motor. On the other hand, when using Hall sensor means, it is well known that magnetic poles are used at the motor shaft that cause Hall signal impulses in the rotation of the motor shaft in order to detect the position of the motor.
In the case of this detection of the position by means of counting impulses or current peaks it has been proven that errors accumulate in the position count, which must naturally be taken into account in order to prevent putting the user of the specific system at risk. It was hence so far customary in such cases to prevent an automatic movement of the driven component from the start or as an emergency solution to end it after a fixed given number of shorter movements (in both directions) even if the desired position or a known position such as for example an end position, was not reached. A considerable disadvantage of this known solution is that the dynamic behavior of the drive systems is not taken into account. For example, when the movement takes place in a controlled manner and no doubtful situations are detected, it is unjustified and disadvantageous for the functioning of the system if the automatic movements are ended without real necessity, which however takes place in the known solutions. On the other hand, when unfavorable situations arise, for instance in the case of EMC interferences or the fast reversal of movement controls, the system can switch over as fast as possible in the operating mode to an emergency stop or a manual control to prevent possible damage to the system or injuries to users by jamming—in this case it would therefore be wrong and dangerous to wait for a fixed given number of movements up to the switchover.